This invention relates generally to combined coupling and braking devices, and more specifically it relates to a clutch combined with a double-action braking device for use in intermittently operating machines such as presses and the like.
For driving such machines, a primary shaft is provided with at least one coupling disk arranged for engagement with a clutch lining on a clutch supporting disk that is secured to the driven shaft of the machine. The clutch supporting disk is usually provided with two opposite, axially movable pressure disks provided with pistons that are actuated by a pressure medium to bring the fricition lining into engagement with the coupling disk. In rest condition, the driven shaft is braked by means of two stationary braking disks and by pressure springs which urge the pressure disks away from the coupling disks and into engagement with the braking disks.
Intermittently operating machines such as presses and the like are equipped with the above-defined clutch and double-acting braking devices mainly for safety reasons, especially to meet the requirements and regulations imposed by labor unions, for example. In the event that one of the combined braking members, usually the spring biased pressure disk engaging the braking disk, becomes accidentally inoperative, the other braking member provided in the machine remains operative and performs the braking function.
Driving units provided with a combined clutch-and-braking devices having an additional brake have been known in the art. In one prior art device of this kind, an additional brake is simply arranged at a distance from the coupling-and-braking unit. A considerable disadvantage of this prior art embodiment results above all from the separate construction of a supporting disk of cylindrical configuration and having relatively thin walls. Since these walls are exposed to large bending forces, a considerable danger of rupture and of a permanent failure is always present. Moreover, such additional braking devices are costly in manufacture and also present increased space requirements for the entire equipment. From the functional point of view, the separately arranged additional brake does not satisfy the requirement for an increased safety against rupture. This disadvantage is common to other known devices of this type.
In another prior art device having only a single brake supporting disk that at one side is provided with a cylindrical space and at the other side with a piston, there result pressure spaces having different sizes. For this reason even this system cannot be considered as satisfactory from the safety point of view. Since the clutch and brake devices have in most cases a very limited space available, it is essentail that the clutch and brake units be designed so as to occupy minimum space. The aforementioned known devices because of their excessively voluminous structure of supporting disks and pressure rings are far from meeting the requirement for a compact design.
Furthermore, the aforementioned prior art devices of this kind, due to their bulky construction of supporting disks and pressure disks arranged at least partially in a housing, have an insufficient area for radiating heat outwardly so that localization of heat takes place which inadvertantly reduces the working life and functional reliability of the device (the packing and the lamination, for example).
In another known modification, two commercially available, combined clutch-and-brake units have been arranged, respectively, at each side of the driving member to provide the required additional brake. In spite of the fact that this arrangement meets the safety requirement, it has the considerable disadvantage that in most cases it has a very limited use in special applications only and moreover, to fulfill the safety measures for the entire equipment an inproportionally high cost has to be expanded.